Analysis of parameter effects on chemical reaction coupled transport phenomena in SOFC anodes

Mass, heat and momentum transport processes are strongly coupled by internal chemical reforming reactions in planar design solid oxide fuel cell (SOFC) anodes. In this paper, a three-dimensional computational fluid dynamics approach is applied to simulate and analyze reforming reactions of methane and various transport processes in a duct relevant for SOFC anodes. The results show that the anode duct design and operating parameters, grouped as three characteristic ratios, are significant for the chemical reactions and further for multi-species distribution, fuel gas transport and heat transfer in the sub-domains of the anode.     

Some remarks on the perturbation and variation–perturbation calculations of the free energy for quantum systems

A generalization of the Gibbs–Bogoliubov inequality F ? F₀ + 〈H ? H₀〉₀ for the free energy F is studied which leads to a variation principle for this quantity that may be of importance in certain computational applications to quantum systems. This approach is coupled with a study of the perturbation expansion of the free energy for a canonical ensemble with H = H₀ + λV in the general case when H₀ and V do not commute. The second- and high-order derivatives of the free energy with respect to the perturbation parameter λ are calculated. From the second-order term is finally obtained a second-order correction to the previous variational minimum for the free energy.     

Nucleic acid-metal interactions. IV. Complexes of Ag(I) with thymine and cytosine from studies of UV and IR dichroic spectra

The linear dichroism of the complexes of thymine and cytosine with silver(I) ions dispersed in stretched polyvinylalcohol films was measured in the infrared and in the near ultraviolet regions of the spectrum. The infrared results were helpful in establishing the orientation of the complexes in the films; they also confirmed that the site of silver binding in the case of cytosine involves the carbonyl oxygen. The ultraviolet spectra were deconvoluted into separate electronic transitions and the corresponding transition moments of silver complexes were determined.     

Accuracy of radial basis function interpolation and derivative approximations on 1-D infinite grids

Radial basis function (RBF) interpolation can be very effective for scattered data in any number of dimensions. As one of their many applications, RBFs can provide highly accurate collocation-type numerical solutions to several classes of PDEs. To better understand the accuracy that can be obtained, we survey here derivative approximations based on RBFs using a similar Fourier analysis approach that has become the standard way for assessing the accuracy of finite difference schemes. We find that the accuracy is directly linked to the decay rate, at large arguments, of the (generalized) Fourier transform of the radial function. Three different types of convergence rates can be distinguished as the node density increases – polynomial, spectral, and superspectral, as exemplified, for example, by thin plate splines, multiquadrics, and Gaussians respectively. Bengt Fornberg: The work was supported by NSF grants DMS-9810751 (VIGRE), DMS-0073048 and DMS-0309803.Natasha Flyer: The work was supported by the NSF grant DMS-9810751 (VIGRE).     

Decomposition of diphenylamine in nitrocellulose based propellants-I. Optimization of a numerical model to concentration-time data for diphenylamine and its primary degradation products determined by liquid chromatography with dual-amperometric detection

The consumption of diphenylamine (DPA) in two nitrocellulose (NC) based propellants subjected to a heat storage test at 85 degrees has been studied. A previously developed method based on reversed-phase liquid chromatography with dual-amperometric detection was used to monitor the concentrations of DPA, 2-nitro-DPA and 4-nitro-DPA during the test. A numerical model based on first order rate equations was fitted to the obtained analytical data with the use of a specially written curve fitting program. The model implemented in the program describes the initial nitrosation and nitration steps of DPA in aging NC propellants. The use of matrices in the calculation of concentration-time (CT) curves enables the introduction of a general algorithm which can be readily changed in order to simulate any system of first order reactions. The program can therefore be used in other applications such as mechanistic studies in organic synthesis. The general simulation algorithm allows inclusion of unknown (not analysed) components in the reaction mechanism. In this application, it was possible to simulate the course of N-nitroso-DPA which is not detectable by the amperometric principle.     

Distribution analysis of ultra-high molecular mass poly(ethylene oxide) containing silica particles by size-exclusion chromatography with dual light-scattering and refractometric detection

Two different size-exclusion chromatography (SEC) systems, connected in-line either to a low-angle light scattering (LALS) or to a multiangle light scattering (MALS) detector, are employed for determination of molecular mass distributions (MMD) of poly(ethylene oxide) (PEO) samples having a weight average molecular mass up to eight millions. The detrimental effect of the presence of strongly scattering silica particles in the samples on the light scattering signal can be eliminated using a suitable sample dissolution procedure utilizing silica solubility in aqueous mobile phase. The selection of flow-rate and sample concentration have a large impact on the obtained results. Hydrodynamic retardation phenomena and nonlinearity effects are shown to introduce severe errors in the molecular mass distributions unless flow-rate and sample concentration are kept at sufficiently low levels. Self-compensating ability of the dual detection in flow-rate effects is shown to be the main advantage here. A good agreement between the results obtained using LALS and MALS detection is found provided that a carefully selected angular extrapolation procedure is used in the case of MALS data. Thus, using carefully selected experimental conditions, SEC with light-scattering (LS) and refractometric detection proved to be an efficient technique for MMD characterisation also of ultra-high molecular mass (UHM) PEO polymers.     

Simulation of proliferation of neural stem cells on a surface with emphasis on spatial constraints on cell division

We present Monte Carlo lattice simulations of proliferation of cells on a surface in the situation when the cell-cell adhesion is relatively strong and the cells may form islands and/or flattened hemispheres. The model parameters were chosen to mimic proliferation of adult rat neural stem cells (or, more specifically, adult hippocampal progenitor cells) deposited on polyornithine and laminin coated polystyrene. The results obtained show that the spatial constraints on cell division may result in slowdown of the exponential growth. Depending on the rules used for cell division, this effect may be either nearly negligible or appreciable. In the latter case, the scale of the deviations from the exponential growth is comparable with that observed in our experiments. In the simulations, the slowdown of the growth starts however somewhat earlier and occurs in a less abrupt manner. This seems to indicate that the spatial constraints on division of cells are not the main factor behind the experimentally observed termination of the growth.     

Photometric determination of quaternary ammonium compounds with hexanitrodiphenylamine. I.

Dissociation contants, partition coefficients and absorption spectra have been determined for hexanitrodiphenylamine and pentanitrodiphenylamine. The two compounds have quite different dissociation constants and can be easily separated. Both substances give compounds with quater- nary ammonium ions which can be extracted with chloroform or methylene chloride from an aqueous solution. to obtain a pure hexanitrodiphenylamine compound the reagent must be free from pentadinitrodiphenylamine and the extraction made at high pH.